Voting Multiplier Hotfix

[RonTuretzky]

• external and public functions should not have an underscore. internal functions should have underscores, and thus would not be part of the interface
• specify import:
  import {IERC721} from "@openzeppelin/contracts/token/ERC721/IERC721.sol";
• should we use Ownable2StepUpgradeable instead? it is safer to use during ownership transfers, but more gas
• missing declared return value.
  _factor = hasNFT(_user) ? FACTOR : 0;
  instead of using return keyword. this applies throughout the repo